The present invention relates generally to a head positional assembly (HPA) for disc drives. More particularly, the present invention relates to a head positional assembly wherein the voice coil of the voice coil motor (VCM) is damped.
Disc drives are used in computer applications for high volume data storage and retrieval. Typically, disc drives contain a head disc assembly (HDA) mounted on a base or disc enclosure. The head disc assembly includes an actuator slider system for transferring data to and from circular tracks concentrically disposed on the surfaces of the disc. Data is transferred to and from the discs as they are rotated at a predetermined speed on a spindle mechanism.
The actuator slider system or head positional assembly (HPA) includes a transducer mounted on a slider for transferring data to and from the disc. The slider is attached to an actuator arm via a gimbal assembly. The actuator arm pivots about the pivotal axis of an E-block assembly. Movement of the E-block assembly and the attached actuator slider system is controlled by a voice coil motor (VCM).
Ideally, the slider should precisely follow the motion of the E-block assembly within the frequency range of interest. This means that movement of the E-block assembly generated by the voice coil motor should be transmitted through the actuator arm, the gimbal assembly and to the slider without any distortion. In such ideal operating conditions, tracking can be performed efficiently and track densities on the disc can be increased. Unfortunately, due to vibrations within the system it is difficult to achieve such ideal conditions of operation. Vibration is a particularly serious problem when it occurs at or near the resonant frequencies of the components of the system.
Undamped, rigid mechanical structures have lower resonant frequencies than damped structures having the same effective stiffness. They also tend to exhibit vibrations of higher amplitude at resonant frequencies. For this reason, an undamped and rigid head positional assembly attains its structural resonance frequencies at lower excitation and also experiences larger amplitude vibrations at its resonance frequencies. These vibrations cause the servo control system of the head positional assembly to fail resulting in deteriorating disc drive performance. It can thus be appreciated that the mechanical structure of the head positional assembly will have a significant effect upon the capability of a disc drive to use discs of high track density.
Several methods have been developed to reduce vibration problems in the head positional assembly. One such method includes providing a damper on the gimbal assembly. However, this method is only effective if the gimbal assembly is the source of the resonance that is causing the vibrational problem.
Another method that has been employed is xe2x80x9cfrequency tuningxe2x80x9d. This involves designing the head positional assembly so that its resonant frequencies are not within the frequency range in which the servo control system of the disc drive is considered to be significantly affected by vibrations. However, it is difficult to predict actual resonant frequencies at the design stage, as resonances can be affected by several factors.
A further method employed has been to damp the pivot bearing on which the head positional assembly is mounted. U.S. Pat. No. 5,666,242 filed Nov. 21, 1995 by Edward et al for DISK DRIVE HAVING ELASTOMERIC INTERFACE IN PIVOT BEARING ASSEMBLY and U.S. Pat. No. 5,675,456 filed Nov. 21,1995 by Myers for ACOUSTIC VIBRATION DECOUPLER FOR A DISK DRIVE PIVOT BEARING ASSEMBLY describe methods of damping vibratory motion imparted to the head positional assembly through the pivot bearing. The former uses an elastomeric interface between the stationary member of the pivot bearing and the head positional assembly. The latter uses axial decoupling between the pivot shaft and the head positional assembly to minimise the transmission of acoustic vibration from the pivot shaft. U.S. Pat. No. 5,790,348 describes a head positional assembly having a cantilevered coil portion to provide damping of vibrations induced in the head positional assembly.
The present invention aims to provide a solution to the vibration problems mentioned above, and offers other advantages over the prior art.
The present invention relates to a voice coil for a head positional assembly of a disc drive. The voice coil includes a dampener which incorporates a constraint material and a viscoelastic material. The dampener is preferably located in the bobbin space.
The constraint material is selected from an aluminium, steel, zinc copper, ceramic, viscoelastic or elastomeric material. The viscoelastic material is preferably a double sided, pressure sensitive material. Vibrations produced in the voice coil are damped by the dampener and thus the head positional assembly is less susceptible to vibrations.
The voice coil is made from a coil of copper wire. Additionally, at least a portion of the voice coil may have a plastics overmold.
The present invention also relates to a disc drive having a head positional assembly including a voice coil and a dampener. The dampener includes a constraint material and a viscoelestic material.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.